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A218420
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Hilltop maps: number of n X 2 binary arrays indicating the locations of corresponding elements not exceeded by any horizontal, vertical or antidiagonal neighbor in a random 0..1 n X 2 array.
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2
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3, 13, 49, 191, 737, 2849, 11011, 42557, 164481, 635711, 2456993, 9496161, 36702211, 141852301, 548252401, 2118969471, 8189716289, 31652864193, 122336815619, 472825977597, 1827449929601, 7063007117695, 27298186799297, 105506194473793
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OFFSET
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1,1
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COMMENTS
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LINKS
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FORMULA
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Empirical: a(n) = 3*a(n-1) + 3*a(n-2) + a(n-3) + a(n-4) + a(n-5).
Empirical g.f.: x*(3 + 4*x + x^2 + 2*x^3 + x^4) / (1 - 3*x - 3*x^2 - x^3 - x^4 - x^5). - Colin Barker, Mar 10 2018
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EXAMPLE
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Some solutions for n=3:
..1..1....0..1....1..1....0..0....0..1....0..0....1..0....1..1....0..1....1..0
..0..0....1..1....0..0....1..1....0..1....1..0....0..0....1..0....1..0....1..0
..0..1....0..1....1..1....1..1....1..1....1..1....1..0....1..0....1..1....1..1
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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